The IEEE 802.3-2005 standard, which is incorporated in-full by reference herein, specifies Ethernet local area network (LAN) operation for selected speeds of operation from 1 Mb/s to 10 Gb/s using a common media access control (MAC) specification, management information base (MIB), and capability for Link Aggregation of multiple physical links into a single logical link. Gigabit Ethernet (GbE) is one particular implementation defined in the IEEE 802.3-2005. GbE is commonly referred to as 1000BASE-X, where -X refers to either -CX, -SX, -LX, or (non-standard)-ZX
In IEEE 802.3-2005 clause 37, Auto Negotiation for 1000BASE-X allows a device (local device) to advertise modes of operation it possesses to a device at the remote end of a link segment (link partner) and to detect corresponding operational modes that the link partner may be advertising. The Auto Negotiation function exchanges information between two devices that share a link segment and automatically configures both devices to take maximum advantage of their abilities. The Auto Negotiation function allows the devices at both ends of a link segment to advertise abilities, acknowledge receipt and understanding of the common mode(s) of operation that both devices share, and to reject the use of operational modes that are not shared by both devices.
Optical transmission systems can be used to provide extended reach between Ethernet clients, such as GbE. For example, these systems can include SONET/SDH network elements, Optical Transport Network (OTN) network elements, dense wave division multiplexing (DWDM), coarse wave division multiplexing (CWDM), and the like with optical amplifiers and repeaters to provide extended reach. Additionally, these systems can also support IEEE 802.3-2005 specifications providing layer two support functionality for Ethernet clients. For example, conventional SONET/SDH/OTN and DWDM/CWDM transponder systems currently support layer two interfaces, such as GbE, and can include Auto Negotiation functionality.
Referring to FIG. 1, a network diagram illustrates an example of Auto Negotiation in steps 10a-e between clients 12,14 connected through wavelength division multiplexed (WDM) 16,18 devices over an optical network 20. The clients 12,14 can include switches, routers, or the like with GbE interfaces to the WDM devices 16,18. The WDM devices 16,18 include line cards capable of receiving GbE interfaces and providing Ethernet capabilities, such as Auto Negotiation. Additionally, the WDM devices 16,18 can include optical amplifiers, optical filters, and the like as are known in the art with regards to optical transmission systems. The optical network 20 represents intervening nodes (not shown) at geographically diverse locations. For example, the optical network 20 can span 8000 km in an exemplary embodiment.
FIG. 1 illustrates Auto Negotiation steps 10a-e according to conventional mechanisms with the optical network 20 spanning 8000 km between the WDM devices 16,18. In this exemplary embodiment, each of the clients 12,14 and the WDM devices 16,18 supports Auto Negotiation. In step 10a, there is a fiber break or other link failure between the client 12 and the WDM device 16. Accordingly, GbE ports on the WDM devices 16,18 are down, and the link between the WDM device 18 and the client 14 is forced down. A secondary backup link 22 can become active between the clients 12,14. The secondary backup link 22 can utilize a different route (i.e., in the event of a fiber break), different equipment (i.e., in the event of an equipment failure), or the like.
At step 10b which is at a time t, the link between the client 12 and the WDM device 16 is back up and running. Here, Auto Negotiation begins between the client 12 and the WDM device 16, and the WDM device 16 sends an Auto Negotiation start message to the WDM device 18 through the optical network 20. At step 10c which is at time t+30 ms, the Auto Negotiation is complete between the client 12 and the WDM device 16 and the link is up with the secondary backup link 22 back in a passive state. Also, the Auto Negotiation start message is received by the WDM device 18 through the optical network 20, and the WDM device 18 begins Auto Negotiation with the client 14. Note, in this example, the Auto Negotiation state machines between the WDM devices 16,18 are spaced apart by a delta time. This delta time represents the transit time through the optical network 20. For example, on the optical network 20 with a link length of 8000 km, the delta time would be approximately 30 ms. This delta time is a function of the latency associated with the optical network 20.
Each of the clients 12,14 and the WDM devices 16,18 are configured to operate Auto Negotiation state machines. For example, IEEE 802.3-2005 defines the Auto Negotiation state machine in FIG. 37-6. The state machine operated at the client 12 is ahead of the state machine at the WDM device 16 because of the distance and associated latency on the optical network 20. Accordingly, the state machine at the client 12 determines success between the client 12 and the WDM device 16 and the link is up at step 10c. This causes the client 12 to stop transmitting on the secondary backup link 22 as it reverts to the primary link between the client 12 and the WDM device 16. Finally at step 10c, the WDM device 18 receives the Auto Negotiation start message, and Auto Negotiation starts between the WDM device 18 and the client 14.
At step 10d which is at a time t+30 ms+30 ms, it is determined that there is an Auto Negotiation error between the client 14 and the WDM device 18. For example, the link between client 14 and WDM device 18 could be set for half duplex while the other links are full duplex. Accordingly, the link between the client 14 and the WDM device 18 is not up, and the secondary backup link 22 is also not up. Here, WDM device 18 sends a link error message to WDM device 16 based on the Auto Negotiation error. At step 10e which is at a time t+30 ms+30 ms+30 ms, the WDM device 16 receives the link error message and sends this to the client 12 which accordingly begins transmitting on the secondary backup link 22 again. Effectively, this process results in a link flagging at client 12 between the primary and secondary link 22 which results in a traffic hit of at least 60 ms.
The Auto Negotiation specification includes a LINK_TIMER which is defined as 10 ms with a tolerance of +10 ms. This is the only timer defined in clause 37 of IEEE 802.3, and it is used throughout the Auto Negotiation process to verify that both link partners have enough time to complete. The tolerance is implementation specific and may not be the same across different system implementations. Generally, a single pass through Auto Negotiation, i.e. a run of the Auto Negotiation state machine, takes approximately 30 ms due to the number of instances LINK_TIMER is operated in the state machine.
Thus, the conventional Auto Negotiation mechanisms can fail when any two client devices are space apart by a delta time such that the route transit time results in one state machine finishing before the other signals a success or failure indication. Any failure to successfully negotiate will only be reported at another client after a minimum of 2× delta time. Disadvantageously, these current mechanisms prevent Auto Negotiation over extended distances as are common with regard to Ethernet clients over optical networks.